Double conductor single phase inductive power transfer tracks

ABSTRACT

An IPT track arrangement including a power supply and conductor electrically connected to the power supply, the conductor includes a plurality of loops located substantially adjacent one another, wherein the polarity in adjacent portions of the loops is the same, and wherein the power supply includes a one or more inverters which share the track load.

FIELD OF INVENTION

The invention relates to Inductive Power Transfer (IPT) systems. Inparticular, the invention relates to an improved track and a pickup foruse with the track.

BACKGROUND

IPT uses a varying magnetic field to couple power across an air gap, toa load, without physical contact. The air gap is present between aprimary conductor such as an elongate loop of conductive material(generally referred to in this document as a track), and one or morepick-up devices that have a secondary coil which receive power from themagnetic field associated with the track. System performance is notaffected by wet or dirty environments and there are no safety risksunder such conditions since the components are completely isolated. IPTis reliable and maintenance free unlike conventional plug or brush andbar contact based methods such as those used on trams and electricbuses. IPT is presently used in numerous industrial applications such asmaterials handling and IC fabrication. The systems vary in capacity from1 W-200 kW and can be used to both power and recharge robots, AutomaticGuided Vehicles (AGV), electronic devices, recreational people movers,buses and Electric Vehicles (EVs). IPT systems may be divided into twodistinct types: distributed systems that consist of one or more movableloads that may be placed anywhere on a track, and lumped systems thatonly allow power transfer at a defined location.

Distributed systems are particularly suited to Roadway Powered EV (RPEV)applications, however practical large scale RPEV systems have so farbeen infeasible. This is due to the large horizontal tolerance (˜700 mm)and ground clearance (150-200 mm) required by unguided EVs. The tracktopology presented in this document offers a significant improvementover previous designs by allowing increased horizontal tolerance withminimal increase to the system cost. Those skilled in the art willappreciate that this document predominantly refers to applications ofthe invention in the context of AGVs, but the invention is applicable tomany other IPT system applications. For example, if ferromagneticmaterials (such as ferrite) are associated with the track arrangementsdisclosed herein, then the invention may have applicability to IPTsystems for EVs and RPEVs.

EVs help reduce dependence on fossil fuels, emission of greenhousegasses and emission of pollutants. Consequently, uptake of EVs has beenincreasing since the 1990's however market penetration has been lowbecause EVs are not as cost effective as conventional vehicles. Thepresent EV market is dominated by hybrid vehicles that derive theirenergy from a combustion engine, however, plug-in EVs (PHEV) haverecently been introduced enabling energy from the grid to mitigategasoline consumption. In order for EVs to gain widespread adoption,major improvements are required in battery life and cost, and gridconnection. The latter allows opportunistic charging after each triprather than a long charge at the end of the day. As a result batterywear is significantly reduced by minimising the depth of discharge andthe EV has a lower cost since a smaller battery is required. Thepreferred solution that makes EVs more cost effective than gasolinevehicles is to power and recharge the EV via the road. It should benoted that the infrastructure for such a dynamic charging system couldbe relatively small because travel on interstate highways makes up 1% ofroadway miles but carries 22% of all vehicle miles travelled. An EV thathas 50% of its driven miles connected to a dynamic charging system wouldbe as cost effective as a conventional vehicle and does not incuradditional gasoline costs.

An IPT system comprises three main components that are shown for asingle phase system in FIG. 1, which is based on an example of use in aroadway. The power supply produces a sinusoidal current (usually in the10-40 kHz frequency range) that drives a current (I₁) in an inductiveprimary conductive path, or track. Although not shown in FIG. 1, thetrack comprises (but is not limited to) part of an LCL network with thetrack inductance L₁ comprising the final “L” of the network. Theparallel compensation capacitor C₁ allows the track current, I₁, toresonate, increasing the magnetic field strength in the vicinity of thetrack. This minimises the VA rating of the power supply for a givenload. The track and Pick Up (PU) act as a loosely coupled transformer,enabling power transfer over relatively large air gaps. The IPT PUinductance, L₂, is tuned for resonance with C₂. This compensates for therelatively large PU leakage inductance. The voltage across C₂ isrectified and a switched mode controller enables the resonant tank tooperate at a defined quality factor, Q, to boost power transfer andprovide a usable DC output. The power output of an IPT system (P_(out))is quantified by the open circuit voltage (V_(oc)) and short circuitcurrent (I_(sc)) of the PU as well as the quality factor as shown in(1).

$\begin{matrix}{P_{out} = {{P_{su}*Q} = {{V_{oc}*I_{sc}*Q} = {{\omega \; M\; I_{1}*\frac{M\; I_{1}}{L_{2}}*Q} = {\omega \; I_{1}^{2}\frac{M^{2}}{L_{2}}Q}}}}} & (1)\end{matrix}$

P_(su) is the uncompensated power, ω is the angular frequency of thetrack current I₂, M is the mutual inductance between the track and PU.As shown in (1), the output power is dependent on the power supply (ωI₁²), magnetic coupling (M²/L₂) and PU controller (Q).

Increasing the power output and separation between the track and PU ishighly desirable but efficiency is limited by the operational frequency(switching loss) and current rating (copper loss) of the system.Allowing a system to operate at a high Q boosts power transfer but inpractical applications it is normally designed to operate between 4 and6 due to component VA ratings and tolerances. Due to these limits, thegreatest increase in system performance can be achieved by good magneticdesign.

In order to improve horizontal tolerance, a three phase track topologyas shown in FIG. 2 (a) has been previously proposed. The vehicle drivesalong the length of the track, Tx, which is referred to as the x-axis.The system uses an inductor-capacitor-inductor (LCL) impedanceconverting network that converts the voltage sourced inverter into acurrent source suitable for driving the inductive track. The leakageinductance of the isolating transformer is used as the first inductorand the track forms the last inductor, so that only real power passesthrough the transformer. Large reactive currents (I₁ in FIG. 1)circulate in the track and capacitor only. Three individual isolatingtransformers connected in a delta-delta configuration were used for eachphase, however the output terminals of the transformers were connecteddirectly to the start and return of each track loop resulting in a sixwire track. This track topology is termed “bipolar” in this documentbecause the PU is exposed to both forward and returning currents to thesupply. The overlapping nature of the track phases results in currentsthat differ by 60° in each adjacent wire and in a similar manner towindings in a cage induction motor, this creates a travelling fieldacross the width (Ty) of the track. This moving field results in a wideand even power profile with a simple single coil PU.

However, a consequence of having overlapping tracks is the presence ofmutual inductance between phases, so that energy from one track phasecouples into adjacent phases, similar to the power coupling between eachtrack conductor and the PU. This cross coupling causes different legs inthe inverter to source large currents and the DC bus voltage surges asenergy is fed into the inverter. Two approaches were shown to solve themutual inductance problem. Firstly the area of overlap between trackloops can be changed to reduce the mutual inductance- however thisresults in a non-uniform track spacing that affects the smoothness ofthe power profile across the width of the track. Secondly, a fluxcancelling approach can be used where transformer coupling is introducedat the start of the track to create coupling between phases that is outof phase with the coupling between the tracks along the length due togeometry. This is implemented by appropriately looping the track throughtoroidal cores at the start. The first technique minimises the effect ofinterphase mutual inductance but resulted in either poorer performancein the coupled PU, while the second has good performance but addedexpense due to the extra magnetic components required.

There is therefore a need to provide a track with an enhanced lateralrange with an improved (e.g. smoother) power profile.

OBJECT OF THE INVENTION

It is an object of the invention to provide an arrangement which atleast ameliorates one or more of the above-mentioned problems, or to atleast provide the public with a useful choice.

BRIEF SUMMARY OF THE INVENTION

In a first aspect, the invention broadly provides an IPT trackarrangement including a power supply and conductor means electricallyconnected to the power supply, the conductor means including a pluralityof loops located substantially adjacent one another, wherein thepolarity in adjacent portions of the loops is the same, and wherein thepower supply includes on or more inverters.

Preferably the inverters share the load on the track arrangement.

Preferably the inverters are electrically connected together inparallel.

Preferably, the conductor means includes a single conductor, wherein, informing the loops, the conductor overlaps itself at a plurality ofpoints.

Preferably, the distance between adjacent loops is substantially smallerthan the width of the loop.

Preferably, the plurality of loops includes at least two loops.

In another embodiment the plurality of loops comprises at least threeloops.

In a second aspect, the invention broadly provides an IPT trackarrangement including a power supply and conductor means electricallyconnected to the power supply, the conductor means including a singleconductor forming a plurality of loops located substantially adjacentone another, wherein the polarity in adjacent portions of the loops isthe same.

Preferably, the power supply includes an inverter.

Preferably, the distance between adjacent loops is substantially smallerthan the width of the loop.

Preferably, the plurality of loops includes at least two loops.

In another embodiment the plurality of loops comprises at least threeloops.

In a third aspect, the invention broadly provides an IPT pickup adaptedto be used with an IPT track arrangement according to the first orsecond aspects, wherein the IPT pickup is adapted to receive bothhorizontal and vertical components of the magnetic flux generated by theIPT track arrangement.

Preferably, the IPT pickup includes one or more of: a quadrature pickup,a DDP pad, a DDPQ pad, a BPRP pad.

In another aspect the invention broadly provides an IPT system,including an IPT track arrangement having a power supply and conductormeans electrically connected to the power supply, the conductor meansincluding a plurality of loops located substantially adjacent oneanother, wherein the polarity in adjacent portions of the loops is thesame, and an IPT pickup.

Preferably the pickup comprises a plurality of coils.

Preferably the pickup is adapted to receive components of magnetic fluxgenerated by the IPT track arrangement that are in spatial quadrature.

Preferably the the power supply includes a plurality of inverterselectrically connected together in parallel.

Preferably the conductor means includes a single conductor forming theplurality of loops.

Preferably, in forming the loops, the conductor overlaps itself at aplurality of points.

Preferably, the distance between adjacent loops is substantially smallerthan the width of the loop.

Preferably, the plurality of loops includes at least two loops.

In another embodiment the plurality of loops comprises at least threeloops. Preferably, the IPT pickup includes one or more of: a quadraturepickup, a DDP pad, a DDPQ pad, a BPRP pad.

In another aspect the invention provides an IPT system track arrangementcomprising a plurality of elongate loops of conductive material whereinthe polarity in adjacent portions of the loops is the same, and having across section substantially as shown in FIG. 12 or FIG. 20.

In other aspects, the invention broadly provides an IPT trackarrangement, an IPT pickup and/or an IPT system substantially as hereindescribed.

Further aspects of the invention will become apparent from the followingdescription.

BRIEF DESCRIPTION OF FIGURES

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying drawings, where:

FIG. 1 is a diagram showing a known arrangement of IPT system componentsfor a single phase track system;

FIG. 2 is a diagram of three-phase IPT track topologies, where (a) isbipolar and (b) is unipolar;

FIG. 3 is a diagram of a three-phase bipolar track;

FIG. 4 is a diagram of the polarity of the track of FIG. 3, as takenalong line 4-4′;

FIG. 4A shows the inverter and LCL network arrangement for implementingthe track of FIG. 3.

FIG. 5 is a diagram of a repeated single-phase track;

FIG. 6 is a diagram of the polarity of the track of FIG. 5, as takenalong line 6-6′;

FIG. 7 is a diagram of a double conductor repeated single-phase track;

FIG. 8 is a diagram of the polarity of the track of FIG. 7, as takenalong line 8-8′;

FIG. 8A shows the arrangement of the inverters and LCL networks for therepeated single phase track of FIG. 7

FIG. 9 is a diagram of a two-phase bipolar track;

FIG. 9A is a diagram showing an arrangement for a two phase bipolartrack (inverters being synchronised 90° out of phase) together with thearrangement for each inverter and LCL network.

FIG. 10 is a diagram of the polarity of the track of FIG. 9, as takenalong line 10-10′;

FIG. 11 is a diagram of a double conductor repeated single-phase trackhaving two conductors;

FIG. 11A shows the arrangement of inverters and LCL networks for thedouble conductor repeated single phase track of FIG. 11.

FIG. 12 is a diagram of the polarity of the track of FIG. 11, as takenalong line 12-12′;

FIG. 13 is a set of graphs showing the (a) open-circuit voltage(V_(oc)), (b) short-circuit current (I_(sc)) and (c) uncompensated power(S_(U)) of the track shown in FIG. 3;

FIG. 14 is a set of graphs showing the (a) open-circuit voltage(V_(oc)), (b) short-circuit current (I_(sc)) and (c) uncompensated power(S_(U)) of the track shown in FIG. 5;

FIG. 15 is a set of graphs showing the (a) open-circuit voltage(V_(oc)), (b) short-circuit current (I_(sc)) and (c) uncompensated power(S_(U)) of the track shown in FIG. 7;

FIG. 16 is a set of graphs showing the (a) open-circuit voltage(V_(oc)), (b) short-circuit current (I_(sc)) and (c) uncompensated power(S_(U)) of the track shown in FIG. 9;

FIG. 17 is a set of graphs showing the (a) open-circuit voltage(V_(oc)), (b) short-circuit current (I_(sc)) and (c) uncompensated power(S_(U)) of the track shown in FIG. 11;

FIG. 18A is a set of graphs showing (a) PTotal, (b) VARTotal and (c)STotal for a series tuned track as shown in FIG. 7;

FIG. 18B is a set of graphs showing (a) PTotal, (b) VARTotal and (c)STotal for a parallel tuned track as shown in FIG. 7;

FIG. 18C is a graph showing the comparison between a four wire doubleconductor repeated single phase track of FIG. 11 and a two phase bipolartrack with 0.29 overlap such as the track of FIG. 9.

FIG. 18D is a set of graphs showing (a) real, (b) reactive and (c) totalpower supplied by each inverter to a paralleled tuned quadrature pick-up(including ferrite effect) operating at 2 kilowatts above a two phasebipolar track with 120 mm track spacing 0.29 overlap (i.e. a trackarrangement corresponding to that shown in FIG. 9;

FIG. 18E is a set of graphs showing (a) real, (b) reactive and (c) totalpower supplied by each inverter to a parallel tuned quadrature pick-up(including ferrite effect) operating at 2 kilowatts above a four wiredouble conductor repeated single phase track with 120 mm track spacing(20 mm between double conductors) i.e. a track corresponding to thatshown in FIG. 11.

FIG. 19 shows a track according to one embodiment of the presentinvention;

FIG. 19A shows an arrangement of three inverters and the LCL networkassociated therewith for the track shown in FIG. 19.

FIG. 19B shows an alternative arrangement for a single phase doubleconductor repeated track, together the inverter and LCL network.

FIG. 20 shows the polarity of the track shown in FIG. 19, as taken alongline 20-20′;

FIG. 21 is a diagram of a flat-E pickup;

FIG. 22 is a diagram of a flat pickup;

FIG. 23 is a side view and a plan view of a magnetic flux receiver pad;

FIG. 24 is a side view and a plan view of the pad of FIG. 23, includinga quadrature coil;

FIG. 25 is a side view and a plan view of an alternative form ofmagnetic flux receiver pad.

DETAILED DESCRIPTION

In this specification, the term “track” is used to refer to the primarycircuit of the IPT arrangement. However this should not be construed aslimiting the invention to use in vehicles or the like.

Track Arrangement

Referring first to FIG. 19, there is shown a track 200 including aconductor 202 connected to a power source 208. Conductor 202 is arrangedso as to form three loops substantially in a plane, although it will beappreciated by those skilled in the art that more or fewer loops may beprovided without deviating from the invention. The loops are formed byconductor 202 overlapping itself at two distinct points 204 and 206 suchthat each of the three loops are substantially the same shape and size,the loops being substantially adjacent one another. The distance betweenadjacent sides is reduced, and may be zero, or another low valuerelative to the width of the loop.

In order to safely operate, conductor 202 must have sufficient crosssectional area for the rated track current, and the resulting cablediameter restricts the spacing between the adjacent cables.Additionally, the cable insulation and any supporting material will addfurther thickness to the cable. For example, a Litz cable ofapproximately 15 mm diameter may be used for track currents of 125 A. Asa result, a spacing of 20 mm may be used between adjacent cables.However, the selection of an appropriate conductor and the appropriatespacing between adjacent conductors will be clear to a person skilled inthe art, and accordingly it is not necessary to go into any furtherdetail here.

In the embodiment shown, the loops are shaped substantially like roundedrectangles, having two substantially elongate straight sides and twosubstantially round sides, where the loops are adjacent one anotheralong their straight sides. The points 204 and 206 are located on therounded sides, nearer the straight sides. It will be appreciated thatthe track layout shown in FIG. 19 is a diagrammatic example. Otherconfigurations may be used.

The power source 208 may include either a single inverter which is ratedto supply the total power of track 200 using a LCL network.

In alternative embodiments (and as depicted in FIG. 19) for example,power source 208 may include a plurality of inverters electricallyconnected together in parallel. Again, an LCL network may be used asshown in FIG. 19A. Preferably, the inverters are identical and aresynchronised so as to be in phase with one another. The inverters aretypically supplied from a common mains supply. As shown, individualrectifiers may be provided for each inverter, and if desired therectifiers may be connected together to form a common DC bus.Alternatively, a single rectifier may be used to provide a common DC buswhich supplies the inverters.

The polarity of track 200 is shown in FIG. 8, taken along line 8-8′ ofFIG. 19. In particular, it can be seen that adjacent portions of theloops share the same polarity. This avoids or reduces the disadvantagescaused by opposition of the magnetic flux in adjacent portions, such asnull spots or low-power zones.

In order to display the beneficial attributes of track 200, a number ofknown track arrangements were simulated and tested. The arrangements andresults will be described in detail below.

Other Arrangements

FIG. 3 shows a three-phase bipolar track. The track 100 consists ofthree extended loops 102A, 102B and 102C, comprising six conductors,each loop intersecting with the other two loops near their distal ends,and again at their proximal ends. The loops 102A, 102B and 102C are eachdriven by an independent inverter 104A, 104B and 104C respectively, andcarry currents which are equal in frequency and magnitude, butelectrically separate in phase by 120°. A rectifier may be used toprovide a common DC bus. The three inverters are equal except for thephase shift, and all three phases are each tuned with an LCL network asshown in FIG. 4A, which provides a constant track current independent ofthe loading on that phase. This is desirable as the portion of the totalload that is born by each phase will change as the position of thepickup changes across the width of the track. The current in each phaseis typically equal and held at least nominally constant by the powersupply as well as the frequency of operation. In some situations phasesmay be controlled individually e.g. to make slight adjustments toaccount for component tolerances.

FIG. 4 shows the polarity of the conductors of track 100, as takenthrough line 4-4′ of FIG. 3. In particular, symbols 108 a and 108 bcorrespond to conductor 102 being in a first phase, symbols 110 a and110 b correspond to conductor 104 being in a second phase and symbols112 a and 112 b correspond to conductor 106 being in a third phase.Symbols 108 a, 110 a and 112 a share the same polarity, and likewisesymbols 108 b, 110 b and 112 b share the same polarity. Phasor diagram114 demonstrates the relative relationship between the various phases.

FIG. 5 shows a repeated single-phase track. Similarly to track 100 shownin FIG. 3, track 120 consists of three extended loops 122, 124 and 126,comprising six conductors. The track loops are each driven by a separateinverter 128, 130 and 132 respectively, and carry currents which areequal in frequency and magnitude, and substantially in phase with oneanother. Unlike track 100, the loops 122, 124 and 126 do not intersect,and are separated by track spacing 134, which may be the same as thewidth of one of the loops.

FIG. 6 shows the polarity of the conductors of track 120, as takenthrough line 6-6′ of FIG. 5. Symbols 122 a and 122 b correspond to thelengths of conductor 122, and similarly for symbols 124 a and 124 b andsymbols 126 a and 126 b, and conductors 124 and 126 respectively. Inparticular, it should be noted that 122 b and 124 a and 124 b and 126 a,each of which correspond to adjacent sides of loops, share the samepolarity. As previously noted in relation to track 200, this avoids orreduces the disadvantages caused by opposition of the magnetic flux,such as null spots or low-power zones.

FIG. 7 shows a double conductor repeated single-phase track. Althoughtrack 140 is similar to track 120 shown in FIG. 5, track spacing 148 issubstantially less than track spacing 134, and may be practically zeroor some small value in relation to the width of the track. The trackloops are driven using an LCL network, as shown in FIG. 8A.

FIG. 8 shows the polarity of track 140, as taken through line 8-8′ ofFIG. 7. Symbols 142 a and 142 b correspond to the lengths of conductor142, and similarly for symbols 144 a and 144 b and symbols 146 a and 146b, and conductors 144 and 146 respectively.

It should be noted that, unlike track 120, the polarity of adjacentlengths of loops of track 140 are the same, that is to say 142 b and 144a, which correspond to adjacent lengths of loops 142 and 144respectively, and 144 b and 146 a which correspond to adjacent lengthsof loops 144 and 146, share the same polarity. This is to prevent mutualcoupling, due to the reduced track spacing 148, however it is envisionedthat track 140 could also have a similar polarity to track 120, wherebyadjacent portions of the track have different polarity.

FIG. 9 shows a two-phase bipolar track. Track 160 consists of twoextended loops 162 and 164, comprising four conductors, the loopsintersecting at their distal ends. The loops 162 and 164 are each drivenby an independent inverter 166 and 168 respectively, and carry currentswhich are equal in frequency and magnitude, but electrically separate inphase by 180°. A rectifier may be used to provide a common DC bus.Inverters 166 and 168 are equal except for the phase shift, and bothphases are tuned with an LCL network which provides a constant trackcurrent independent of the loading on that phase. This is desirable asthe portion of the total load that is born by each phase will change asthe position of the pickup changes across the width of the track. Thecurrent in each phase is equal and held constant by the power supply aswell as the frequency of operation. The phases are driven by LCLnetworks as shown in FIG. 9A.

FIG. 10 shows the polarity of track 160, as taken through line 10-10′ ofFIG. 10. Symbols 170 a and 170 b correspond to conductor 162 and symbols172 a and 172 b correspond to conductor 164. Phasor diagram 174 showsthe relationship of the phases of track 160. Again, the loops are drivenusing LCL networks as shown in FIG. 11A.

For better comparison with track 160, a two-loop double conductorrepeated single-phase track is shown in FIG. 11. Track 180 issubstantially similar to track 140, except that there are only twoconductors, 182 and 184, forming two loops.

FIG. 12 shows the polarity of the conductors of track 180, as takenthrough line 12-12′ of FIG. 11. Symbols 182 a and 182 b correspond tothe lengths of conductor 182, and symbols 184 a and 184 b correspond tothe lengths of conductor 184.

Comparisons

Referring now to FIGS. 13 to 17, there are shown graphs of open-circuitvoltage (V_(oc)), short-circuit current (I_(sc)) and uncompensated power(S_(U)), showing the variation along the width of the track, for each oftracks 100, 120, 140, 160 and 180 respectively. A quadrature pick-upstructure (see FIGS. 21 and 22) was used for the purposes of making thecomparisons, at a height of 20 mm above the track. Pick-up structuresare discussed further below.

Although it will be clear to those skilled in the art, it may bebeneficial to have a smooth S_(U) across a width of the track, to allowa pickup to be positioned at some offset from the centre. This may haveparticular relevance to pick-ups used in EVs, but also more generally.

It should further be noted that each graph shows the different spatialcomponents of flux received by the quadrature pick-up structure of FIGS.21 and 22. For convenience thus components are referred to as horizontaland vertical components of the magnetic field. These components areshown separately in each graph, as well as the total (i.e. the highestcurve). As will become clear below, it may be beneficial for a pickup tobe able to pick up both components, and therefore reference willgenerally be made to the total outputs, rather than the horizontal orvertical outputs. Pick-ups which make use of both horizontal andvertical components will be described below.

Turning specifically to FIGS. 13 to 15, it can be seen that track 100and track 140 display generally superior power profiles when compared totrack 120, in the sense that the maximum S_(U) for track 120 is limitedto less than 300 VA, whereas track 100 and track 140 have a much greaterS_(U), albeit at the cost of some lateral range.

This reduced lateral range could be compensated in single-phase trackssuch as track 140, for example by adding additional loops, with littleadded complexity. It can therefore be seen that there is little benefitgained from using track 120 over track 100 or track 140.

The output profiles of track 100 and track 140 are substantiallysimilar. As poly-phase tracks, such as track 100, require extracompensation for the mutual inductance between phases, a single-phaselayout may be preferred for many applications. Track 140 thereforedisplays significant benefits.

Turning now to the graphs in FIGS. 16 and 17, it can be seen that track180 displays a generally superior power profile to track 160, and asomewhat greater lateral range. There is therefore clearly a benefit tousing the single-phase track 180, rather than the two-phase track 160.

On the whole therefore, it can be seen that single-phase tracks showgenerally superior power profiles, improved Su and a more flexiblewidth. Further, within single-phase tracks, a double conductor repeatedsingle-phase arrangement, such as track 140 and track 180, may begenerally preferred over the alternatives. This is shown in FIG. 18Cwhich shows a comparison between a four wire double conductor (i.e. twoloop) repeated single phase track and a two phase bipolar track with0.29 overlap.

Power Source

As shown in FIG. 7, each of loops 142, 144 and 146 may be connected toseparate inverters 150, 152 and 154 respectively.

However, referring now to FIG. 18A showing results for a series tuned,pick-up (which reflects an inductive load onto the track) and FIG. 18Bshowing the results for a parallel tuned track pick-up (which reflects acapacitive load onto the track). The track arrangements each have threeseparate inverters. It can be seen from the Figures that the use ofseparate inverters is not preferable. In particular, it can be seen,particularly at the edges of the lateral range, that inverters 150 and154 may need to be rated for a greater output than the total output,which may lead to increased costs in manufacturing the system. Further,as each loop is powered by a single inverter, the failure of any one ofthe inverters may compromise the system as a whole, by introducing nullzones. FIG. 18D shows real, reactive and total power supplied by eachinverter to a parallel tuned quadrature pick-up above a two phasebipolar track; FIG. 18E shows real, reactive and total power supplied byeach inverter to a parallel tuned quadrature pick-up above a four wiredouble conductor repeated single phase track. It can seen that the VARload on the two phase track is quite undesirable, with the capacitiveload on one inverter and an inductive load on the other, reaching + or−300 VAR over the + or −50 mm operating range. In comparison, the VARload on the double conductor repeated single phase track is a smoothcapacitive load profile of −200 VAR per track loop. It is clear that thedouble conductor repeated single phase track is preferable for trackswith four conductors.

An alternative track arrangement is shown in FIG. 19. Track 200 isformed of a single conductor 202. Conductor 202 is arranged so as toform three loops (although, more or fewer loops may be used, as would beclear to those skilled in the art). This is done by conductor 202overlapping itself at points 204 and 206, however the position of points204 and 206 is not fixed, and may be at any appropriate location alongconductor 202. As the overlap necessarily increases the height of thetrack at those points, track 200 may require additional verticalclearance. The distance between adjacent portions of the conductor maybe reduced to a smaller value, so as to retain the benefits of thedouble conductor repeated single-phase track as previously detailed.

Conductor 202 is attached at its ends to power source 208. Power source208 will preferably include a number of inverters connected in parallel.This adds resilience to the system, in that should one of the invertersmay fail, the remaining functional inverters will be able to take on agreater load to avoid the system being compromised.

Track 200 will have the same power output as track 120, however as theinverters are connected in parallel, each inverter need only be rated totake a fraction of the total load. For example, if there are threeinverters (as shown in FIG. 19 by way of example), each inverter needonly be rated to take about one-third of the total load. This may reducecosts in manufacturing the system, by allowing the use of lower ratedcomponents. Thus one or more inverters may be used to share the loadacross the loops (whether the loops are formed using a single conductoror multiple conductors) that form the repeated single phase trackarrangement.

Power source 208 may also be limited to a single inverter, which needonly be rated to take the whole load, avoiding the problem with track120. An analogous track formed from two loops is shown in FIG. 19B.

Pickup

As previously noted, it may be beneficial to use a pickup adapted tomake use of both the components of magnetic flux that are in spatialquadrature (referred to herein for convenience as the horizontal andvertical components of the magnetic flux) generated by the IPT track, asopposed to standard pickups which make use of only one component.

The simplest of these is known as a quadrature pickup, which is achievedby winding two coils on the pickup core.

There are two ways of achieving the quadrature winding. The first is towind the second coil physically in quadrature with the first coil, whichrequires the use of a flat-E core 5, as shown in FIG. 21. The secondoption is to wind two individual coils on a standard flat core 6, one ateach end, as shown in as shown in FIG. 22. If these coils are connectedin series but 180° out of phase, they will also allow the capture of thevertically oriented flux. Regardless of which topology is chosen, eachof the quadrature coils can be individually tuned, their outputscombined and the output controlled with a single switched-modecontroller.

Referring to FIG. 23, a magnetic flux pad construction previouslydisclosed by Boys, Covic, Huang and Budhia is shown which has excellentcharacteristics suitable for vehicle applications. The construction ofFIG. 23 has been published in international patent publicationWO2010/090539A1. For convenience, this general construction is referredto herein as a DDP pad.

The DDP pad shown in FIG. 23 generally comprises two substantiallycoplanar coils referenced 52 and 53 which are magnetically associatedwith and sit on top of, a core 54. The pad will in practice be invertedso that the coils face the primary track. As can be seen from the FIG.23, the core 54 may consist of a plurality of individual lengths ofpermeable material such as ferrite strips or bars 55 which are arrangedparallel to each other but spaced apart. The pad construction mayinclude a spacer 56 on which the core is located, and a plate 57 belowthe spacer. In some embodiments a cover 58 may be provided on the othersurface of the flat coils 52 and 53. Padding 59 may be provided aboutthe periphery of the pad. As can be seen, the coils 52 and 53 eachdefine a pole area 60 and 61 respectively. This DDP pad construction asshown in FIG. 23 may be used as a flux receiver which may be used in aPU for the track topologies described in this document.

Turning now to FIG. 24, the DDP construction of FIG. 23 is shown butfurther including a quadrature coil 62 (referred to herein as a DDPQpad). This construction is also described in patent publicationWO2010/090539A1. The quadrature coil extends the power transfer profilewhen there is lateral movement of the construction shown in FIG. 24 withrespect to a flux generator such as the DDP pad of FIG. 23 whenenergised by an appropriate inverter. The quadrature coil allows powerto be extracted from the “vertical” component of the magnetic field thatthe receiver pad intercepts while the other coils 52, 53 facilitatepower extraction from the “horizontal” component of the fluxintercepted. Therefore, the construction of FIG. 24 is suited as a fluxreceiver which may be used in a PU for the track topologies described inthis document.

Turning now to FIG. 25, another flux receiver construction is shownwhich is referred to in this document as a bi-polar receiver pad or,alternatively, as a BPRP. The BPRP pad has a similar construction to theDDP discussed with respect to FIGS. 23 and 24 above. In one embodimentthe BPRP pad consists, from bottom up, of an aluminium plate 57, adielectric spacer 56, a core 54 comprising four rows of ferrite bars 55(referred to herein as ferrites), two flat substantially coplanar, yetoverlapping and ideally “rectangular” shaped coils 52, 53 (although inpractice these are more oval due to the ease in winding Litz wire)spread out in the lateral direction, and a dielectric cover 58. The core54 acts as a shield so that ideally all flux is channelled through thecore 54 through the top of the pad. The plate 57 merely acts to a)eliminate and small stray or spurious fields that may be present abovethe core 4 in certain environments, and b) provide additional structuralstrength.

The magnetic structure of the BPRP is designed so that there issubstantially no mutual coupling between either of the coils 52, 53 inthe primary. This allows the coils to be tuned independently at anymagnitude or phase without coupling voltage into each other, which ifpresent would oppose the power output of such a coil. Each coil can beindependently tuned and regulated without affecting the flux capture andpower transfer of the other coil. Thus the BPRP is suited as a fluxreceiver which may be used in a PU for the track topologies described inthis document.

Although the pick-up structures described above with reference to FIGS.23 to 25 use strips of ferromagnetic material, it will be appreciatedthat the amount and arrangement of ferromagnetic material may varysignificantly depending on the required application. For example, insome embodiments there may be no ferrite, and in others there may be afull sheet.

Unless the context clearly requires otherwise, throughout thedescription, the words “comprise”, “comprising”, and the like, are to beconstrued in an inclusive sense as opposed to an exclusive or exhaustivesense, that is to say, in the sense of “including, but not limited to”.

The entire disclosures of all applications, patents and publicationscited above and below, if any, are herein incorporated by reference.

Reference to any prior art in this specification is not, and should notbe taken as, an acknowledgement or any form of suggestion that thatprior art forms part of the common general knowledge in the field ofendeavour in any country in the world.

The invention may also be said broadly to consist in the parts, elementsand features referred to or indicated in the specification of theapplication, individually or collectively, in any or all combinations oftwo or more of said parts, elements or features.

Wherein the foregoing description reference has been made to integers orcomponents having known equivalents thereof, those integers are hereinincorporated as if individually set forth.

It should be noted that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications may be madewithout departing from the spirit and scope of the invention and withoutdiminishing its attendant advantages. It is therefore intended that suchchanges and modifications be included within the scope of the invention.

1. An IPT track arrangement including a power supply and conductor meanselectrically connected to the power supply, the conductor meansincluding a plurality of loops located substantially adjacent oneanother, wherein the polarity in adjacent portions of the loops is thesame, and wherein the power supply includes one or more inverters.
 2. AnIPT track arrangement as claimed in claim 1 wherein the power supplyincludes a plurality of inverters arranged to share the load on thetrack arrangement.
 3. An IPT track arrangement as claimed in claim 2wherein the inverters are electrically connected together in parallel.4. An IPT track arrangement as claimed in claim 1 wherein the conductormeans includes a single conductor, and wherein, in forming the loops,the conductor overlaps itself at a plurality of points.
 5. An IPT trackarrangement as claimed in claim 1 wherein the distance between adjacentloops is substantially smaller than the width of the loop.
 6. An IPTtrack arrangement as claimed in claim 1 wherein the plurality of loopsincludes at least two loops.
 7. An IPT track arrangement as claimed inclaim 1 wherein the plurality of loops comprises at least three loops.8. An IPT system including an IPT track arrangement having a powersupply and conductor means electrically connected to the power supply,the conductor means including a plurality of loops located substantiallyadjacent one another, wherein the polarity in adjacent portions of theloops is the same, and an IPT pickup.
 9. An IPT system as claimed inclaim 8 wherein the IPT pickup includes a plurality of coils.
 10. An IPTsystem as claimed in claim 8 wherein the IPT pickup is adapted toreceive components of the magnetic flux generated by the IPT trackarrangement that are in spatial quadrature.
 11. An IPT system as claimedin claim 9 where one coil is adapted to receive a first component ofmagnetic flux generated by the IPT track arrangement and another coil isadapted to receive a second component of magnetic flux generated by theIPT track arrangement, the components being in spatial quadrature. 12.An IPT system as claimed in claim 11 wherein two coils are adapted toreceive the first component and one coil is adapted to receive thesecond component.
 13. An IPT system as claimed in claim 9 wherein thecoils are mutually decoupled.
 14. An IPT system as claimed in claim 8wherein the power supply includes a plurality of inverters arranged toshare the load on the track arrangement.
 15. An IPT system as claimed inclaim 8 wherein the conductor means includes a single conductor, andwherein, in forming the loops, the conductor overlaps itself at aplurality of points.
 16. (canceled)